Integrated circuits or chips are manufactured with large numbers of identical circuits on a single wafer which ultimately are separately cut from the wafer for use. It is necessary to test each circuit individually to determine whether or not it functions as intended before separating it from the wafer.
Conventional testing employs a probe card which is provided with a large number of small tungsten blades or needles that are mechanically and electrically connected to a circuit board and act as contacts. Electrical leads extend from the contacts to the outer edge of the board for connecting the probe card to test circuitry. In use, the blades or needles are moved into engagement with the pads of an integrated circuit. This provides an electrical connection so that signals can be read to determine the integrity of the circuit on the chip.
The needles or blades must all fall in the same plane in order to assure that each one makes electrical contact with a contact pad of the integrated circuit. This is accomplished by bending the blades or needles after they are mounted on the probe card, which is laborious, time consuming and expensive. Even after such adjustment the blades or needles tend to creep back toward their original positions so that their adjusted locations are lost. This loss of adjustment also comes about from the pressure of the needles against the chips, aggravated by the scrubbing action used to assure penetration of any oxide coating. As a result, constant maintenance is necessary or the probe cards will not perform their intended function. Even when in proper adjustment, the needles cannot compensate for significant differences in the heights of the contact pads on the integrated circuit chips being tested. The needles also may apply excessive forces against the chips so as to damage the chips. The close spacing necessary for testing some chips cannot be achieved with conventional needle contacts.
U.S. Pat. No. 5,148,103 granted to John Pasiencznik Sep. 15, 1992, discloses an improved testing arrangement using a test probe that includes a flexible visually clear and self planarizing membrane. Air pressure behind the membrane is regulated to press probe contacts of the membrane into engagement with the contact pads of the integrated circuit being tested.
U.S. Pat. No. 5,264,787 granted to Blake F. Woith et al. Nov. 23, 1993, discloses another improved testing arrangement using an improved test probe that assures good electrical connections with the contact pads of the integrated circuit chip while avoiding considerable contact of the membrane with other portions of the chip. This improved test probe utilizes a support form behind the membrane to press the probe contacts of the membrane into engagement with contact pads of the integrated circuit being tested. Three embodiments are disclosed including an embodiment using a rigid glass plate as shown in FIG. 9 of the patent.
U.S. Pat. No. 5,461,326 granted to Blake F. Woith et al. Oct. 24, 1995, discloses a further improved test probe that also utilizes a support form behind the membrane. This support is self-leveling and self tensioning.
As noted in the patent, it is important in the use of the membrane test probe that the membrane itself be properly tensioned and configured, because the membrane, which is effectively stretched across the inner area of an annular support, tends to sag or stretch in a haphazard manner. Moreover, because test probe contacts or contact pads on a device to be tested are not all of the same height, good electrical contact may not be accomplished between all test probe contacts and all contact pads of the device under test. Further, because of the curvature of the membrane, the plane of the group of probe test contacts carried by the membrane may not be precisely parallel to the plane of the contact pads of the device under test. Moreover, the test apparatus and the device under test are not necessarily precisely parallel with one another so that the plane of the probe test contacts may be at times slightly inclined to the plane of the contact pads of the device under test.
Accordingly, it is an object of the present invention to provide a membrane test probe that avoids or minimizes above-mentioned problems.